Crystallization and morphology of fibers prepared from compatibilized blends of polyethylene with a liquid crystalline polymer

Abstract

Fibers prepared by melt spinning of compatibilized blends of high-density polyethylene (HDPE) with a semiflexible liquid crystalline polymer (LCP) SBH 1 : 1 : 2 of Eniricerche, Italy, have been investigated by differential scanning calorimetry (DSC) and optical microscopy. Two grades of HDPE with different molar mass have been used to prepare the blends. The compatibilizers are an acrylic acid functionalized polyethylene (Escor 5 000 by Exxon) and an ad hoc synthesized graft copolymer of the liquid crystalline polymer grafted to Escor 5 000 (PE-g-SBH). The studies cover the non-isothermal and isothermal crystallization, and the morphology of the fibers. The influence of the matrix molar mass and the maximal draw ratio of the fibers upon PE crystallization rate have been established. It has been shown that the overall PE crystallization rate under non-isothermal and isothermal conditions increases for fibers prepared from blends of lower molar mass HDPE, compatibilized by PE-g-SBH copolymer. The dispersed LCP phase in the latter fibers due to the enhanced interfacial adhesion in the presence of the copolymer compatibilizer appears as fibrils with high aspect ratio. The results have been interpreted by an increase in interfacial area between the SBH fibrils and the matrix phase, which enlarges the number of heterogeneous nuclei and increases the PE nucleation rate. These effects are less pronounced for the fibers compatibilized with Escor, due to the lower draw ratio of the fibers and to the lower aspect ratio of the SBH fibrils.